I have a project that has a ton of spreadsheet charts in it that I print to PDF to place in an InDesign layout. The client gives me edits that I have to make in my OO file. Every time I open the document, the cell borders revert to a default and I have to change them to my preferred weight before printing to PDF. Why do the border widths not get saved when I change them and save the file? With this many charts and edits, that extra step and time is really a pain in the you-know-what!

What document format are you saving to? Saving to any format other than OOo's native ODF format (.ods for spreadsheets) carries some risk of losing formatting. If you're not saving as ODF, try that and see if you still have a problem.

Also, I believe there are different ways to set the border, or rather, different borders that can be set for an embedded object like a chart. What steps are you following to set the border?